The long term goals of this proposal are to understand the role of apoptosis in the pathogenesis of HIV-related immunodeficiency. The sponsor~s laboratory has long experience in the study of lentiviruses that cause AIDS, with a major focus on humoral immunity and mechanisms of pathogenesis. The co-sponsor's laboratory has characterized some of the intracellular signal transduction pathways in which the activation of a sphingomyelinase hydrolyzes sphingomyelin to ceramide and leads to cell death by apoptosis. Our preliminary studies have shown that HIV-induced apoptosis is accompanied by activation of the ceramide lipid pathway. These results suggest but do not establish that the ceramide pathway may act as a transducer of the effects of HIV products inducing cell death by apoptosis. Therefore, the goals of this proposal are to gain a better understanding of the mechanisms of HIV-induced apoptosis and to explore the role of the ceramide pathway in this process. The project will be divided in two phases. Phase I will consist of two components; didactic and experimental work in the specific areas of vital molecular biology and lipid biochemistry. The aim of the experimental component is to confirm and extend my preliminary observations that the ceramide pathway is activated during HIV-induced apoptosis. Phase II will characterize the structural specificity for the action of HIV or some of its determinants in the activation of the ceramide pathway. The specific aims of this phase are: a) Determine whether intracellular Virus gene expression is required for apoptosis to occur, or whether exogenous viral determinants can trigger apoptosis extracellularly, b) Determine if HIV fusion and syncytia formation are necessary for HIV-induced apoptosis and activation of the ceramide pathway, c) Determine if apoptosis induced by env products is associated with activation of the ceramide pathway, d) Identify env epitopes involved in the induction of apoptosis, e) Explore mechanisms by which HIV or env products interact with T-cell receptors and activate the ceramide pathway.Through the use of these strategies we expect to better define the pathways involved in HIV-related apoptosis and ultimately facilitate design of therapeutic interventions to prevent HIV-induced apoptosis.